FIG. 11 shows a general raster-scan type electron-beam exposure apparatus.
An electron beam emitted from an electron source 101 forms an image 103 of the electron source 101 by an electromagnetic lens 102. The electron source image 103 is reduce-projected onto a wafer 109 via a reduced electron optical system including electromagnetic lenses 105 and 108. A blanker 104, which is an electrostatic deflector in the position of the electron source image 103, controls irradiation and blocking of an electron beam to the wafer 109. That is, when the electron beam is emitted to the wafer 109, the electron beam is emitted on the wafer 109 without the blanker 104. On the other hand, when the electron beam to the wafer 109 is blocked, the electron beam is deflected by using the blanker 104, and the electron beam is blocked by a blanking aperture 106 positioned above a pupil of the reduced electron optical system. Further, the electron beam is scanned by an electrostatic deflector 107.
Next, a method of drawing on the wafer 109 by raster scanning will be described with reference to FIG. 12. For example, when a pattern “A” is to be drawn, first, a drawing area is divided into plural pixels 201. Then, irradiation and blocking of an electron beam 202 is controlled while the electron beam 202 is scanned in a direction X by using an electrostatic deflector, thereby, the electron beam is emitted on only a pixel 203 corresponding to a pattern portion to be drawn. When the X-directional scanning has been completed, the electron beam 202 is stepped in a direction Y, then, similar X-directional scanning is performed. Thus, the entire pattern “A” is drawn. (See, for example, Japanese Patent Application Laid-Open No. Hei 09-245708 and “Electron and Ion beam Handbook”, Japan Society for Promotion of Science, the 132nd Meeting Edition, The Nikkan Kogyo Shimbun, Ltd., page 519.)
However, when a pixel is exposed to a raster-scanned electron beam, the position of the electron beam in the pixel changes with time in the raster scanning direction (direction X), while it does not change with time in the direction vertical to the raster scanning direction (direction Y), as shown in FIG. 13A. That is, as shown in FIG. 13B, the beam current intensity distribution in the pixel in the raster scanning direction (direction X) is the moving average of the electron beam in the pixel. FIG. 13C shows the beam current intensity distribution in the pixel as a result. Accordingly, even in a case wherein the beam current intensity distribution is an axisymmetric Gauss distribution, when drawing is made by raster scanning, the beam current intensity distribution spreads in the raster scanning direction (direction X) as if the electron beam is defocused in that direction. Accordingly, desired pattern dimensional accuracy cannot be obtained without difficulty.
Further, in a case wherein the electron beam has astigmatism aberration or coma aberration due to influence of an electromagnetic lens, a deflector, or the like, and the beam current intensity distribution is not a Gaussian distribution, a desired pattern dimensional accuracy cannot be obtained without difficulty. This problem occurs regardless of raster scanning exposure.